Axial piston engine having an adjustment unit for electrically proportionally adjusting the supply volume

ABSTRACT

The invention relates to an axial piston engine having a swash plate, or a bent axis with a valve segment, which can be adjusted by means of a servo piston, and having an adjustment unit for electrically proportionally adjusting the supply volume. The adjustment unit has a regulating piston for controlling the oil pressure which moves the servo piston, electrically actuable proportional magnets which act on the regulating piston, and a feedback device for feeding the instantaneous swash plate position or bent axis valve segment position back to the regulating piston. The feedback device has a tappet which is mechanically coupled to the swash plate or to the bent axis valve segment, in each case one leaf spring being arranged in the longitudinal direction at both sides of said tappet, said leaf springs enclosing a feedback lever which is mounted in the regulating piston.

BACKGROUND OF THE INVENTION

The invention relates to an axial piston engine having an adjustmentunit for electrically proportionally adjusting the supply volumeaccording to the features of claim 1, and to a type series of axialpiston engines having different supply volumes according to claim 13.

Axial piston engines such as hydraulic pumps and motors, of bothopen-circuit and closed-circuit type, and both of swash plate design andbent axis design, are often operated with electrically proportionaladjustment. The input signal into said adjustment unit is an electriccurrent. Its output signal is a hydraulic pressure. The oil pressurewhich is output acts on servo pistons of the axial piston engine, saidservo pistons being displaced along their movement axes as a result.Said movement is transmitted to a swash plate or to a bent axis valvesegment, which permit variable adjustment of the axial piston enginethrough variation of their angular position.

To regulate the axial piston engine to the value of the supply volumeset by the adjustment device, relevant systems have a regulating pistonwhich is moved by means of at least one proportional magnet, but isgenerally displaced along its movement axis by means of two proportionalmagnets which are arranged opposite one another at the end faces of saidregulating piston, and said regulating piston as a result connecting orblocking ducts such that oil at a certain pressure is available fordisplacing the servo piston.

The mechanical regulator which is conventionally provided is composed ofa lever and spring system, which ensures that, when the set value isreached, the regulating piston is returned to its initial position bymeans of a spring force which is directed counter to the setting forceof the 35 proportional magnets. For this purpose, for example, thesetting movement of the servo piston which is connected to the swashplate is fed back to the regulating valve, or the instantaneous positionof the swash plate or of the bent axis valve segment is fed backdirectly to the electrically operated adjustment unit via a feedback pinwhich is fastened to said swash plate or bent axis valve segment. Saidposition feedback closes the regulating circuit, and ensures that thesupply volume of the axial piston engine is proportional to the electriccurrent to the adjustment unit.

An axial piston engine having a device for adjusting the supply volumeis known from DE 24 56 381 A1, said device comprising a regulatingpiston (“slide valve”) which can be displaced in two directions along acommon axis by means of electromagnets. Here, the control edges of theslide valve alternately connect the lines leading to the piston of aservo motor to discharge and pressure lines, resulting in the piston ofthe servo motor being displaced in one or the other direction and in thesupply volume of the pump being correspondingly adjusted. The piston ofthe servo motor is connected to the slide valve via a return springwhich acts as a tension and compression spring. The force of the returnspring, which increases during adjustment, finally returns the slidevalve and the electromagnets into their initial positions.

The document DE 102 20 889 B3 describes an adjustment device forhydrostatic piston engines. The tappet of a proportional magnet openspressure lines for adjusting a servo piston (“setting piston”) which isin turn connected to the regulating piston via a setting lever which isformed in the manner of a pair of tongs. When the setting piston isadjusted, the arms, which are formed in the manner of a pair of tongs,of the setting lever are spread apart counter to the spring force of atension spring until force equilibrium is reached, a feedback forcebeing generated which acts counter to the control force of theproportional magnet. When force equilibrium has been achieved, theregulating piston is situated in a deflected position such that theservo pressures are in equilibrium with the external forces acting onthe servo piston.

All the known systems require several levers and springs. Productiontolerances and friction losses between the individual parts have anadverse effect on the sensitive force equilibrium. In addition, anindividually dimensioned adjustment unit must be provided for eachinstallation size of a type series.

SUMMARY OF THE INVENTION

The invention is therefore based on the object of producing an axialpiston engine having a simplified, universally applicable adjustmentsystem.

According to the invention, said object is achieved by means of an axialpiston engine having a swash plate, or a bent axis with a valve segment,which can be adjusted by means of a servo piston, and having anadjustment unit for electrically proportionally adjusting the supplyvolume.

The adjustment device comprises a regulating piston for controlling theoil pressure which moves the servo piston, electrically actuableproportional magnets which act on the regulating piston, and a feedbackdevice for feeding the instantaneous swash plate position or bent axisvalve segment position back to the regulating piston, the feedbackdevice having a tappet is which is mechanically coupled to the swashplate or to the bent axis valve segment. In each case one leaf spring isarranged along each side of the tappet, said leaf springs enclosing afeedback lever which is mounted in the regulating piston. This resultsin a comparatively simple construction, with the “pivot angle”regulating variable being fed back directly to the regulating piston.

The leaf springs preferably have a width and/or stiffness which vary, inparticular continuously, in the longitudinal direction of the tappet.This both provides a sufficient material thickness in the fasteningregion of the spring, and simultaneously permits fine-tuning of thestiffness of the leaf spring as a result.

For the purpose of optimizing the force transmission, one end of thefeedback lever is mounted in a ball guide in the regulating piston, andthe feedback lever head, which is situated opposite said end, is clampedbetween the leaf springs. The latter extend along the tappet and beyondits end, and between them, at their ends, form a space for holding thefeedback lever, the feedback lever head preferably being spherical orcylindrical.

In a refinement of the invention, the leaf springs are fastened to thetappet by means of in each case at least one setting screw in such a waythat in each case one preload, with which the leaf springs act on thefeedback lever, can be set by means of the setting screws, said preloaddefining a dead band. The width and/or stiffness of the leaf springspreferably vary in the longitudinal direction of the tappet in thedirection of the feedback lever in such a way that a desired dead bandcan be obtained, that is to say that a correspondingly increased forcelevel in order to move the regulating piston out of its neutral positioncan be provided. This is significant inter a/ia when gravity influenceshave an effect (for example where assembled vertically). Withoutcorresponding preload, the system would pivot out, even if no externalsignal were applied. Another possibility for generating a dead band isto provide an idle stroke of the regulating piston in which the servosare connected only to the tank.

It is particularly advantageous if the dead band of each leaf spring canbe set individually. This can be set particularly effectively if thetappet has screw-on faces on the tappet, said screw-on faces forming acontact surface for fastening the leaf springs by means of fasteningscrews, and a gap, by means of which the preload of the leaf springs canbe set using the setting screws.

The engagement point of the feedback lever in the regulating piston ispreferably situated outwith the central longitudinal axis of the latterand on the longitudinal axis of actuating elements which are actuated bythe proportional magnets (12, 12′). This avoids undesired tiltingmoments.

In a refinement of the invention, the regulating piston has alongitudinal bore. Any leakage oil can be easily discharged through saidlongitudinal bore.

The invention also relates to a type series of axial piston engineshaving 30 different supply volumes, with all the models of said typeseries being provided with the same adjustment unit.

Further features and advantages of the invention can be gathered fromthe following description of an exemplary embodiment.

BRIEF DESCRIPTION OF THE DRAWINGS

In the figures:

FIG. 1: shows an exemplary embodiment of the feedback device of an axialpiston engine according to the invention,

FIG. 2: shows the adjustment device in section along the regulatingpiston,

FIG. 3: is a detail illustration from FIG. 2,

FIG. 4: shows a view of the feedback device with the mounting of thefeedback lever,

FIGS. 5 a, 5 b: are illustrations of the fastening of the leaf springs.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows an exemplary embodiment of the feedback device I of anaxial piston engine according to the invention in a perspective view.The regulating piston 2 is acted on at the end sides by two proportionalmagnets (not illustrated), and can be displaced in its longitudinaldirection in this way. Control edges are formed, in the known way, atthe periphery is of said regulating piston 2, said control edges formingthrottle points with grooves formed in a bore which holds the regulatingpiston, said throttle points being variable as a function of the axialposition of the regulating piston. In this way, hydraulic ducts whichsupply oil at a certain pressure to the servo system (not illustratedhere) for displacing the servo piston are connected or blocked. A swashplate is mechanically coupled to the servo piston, the angular positionof said swash plate being determined by the position of the servopiston.

The illustrated feedback device 1 feeds the angular position of theswash 25 plate back to the regulating piston 2. For this purpose, atappet 9 is provided which, at its mounting end 11, is connected to theswash plate and follows the pivoting movement of the latter. The tappet9 therefore reflects the actual value of the angular position, that isto say the regulating variable of the regulating system. 30

Screw-on faces 16 are formed on the tappet 9, leaf springs 6, 6′ beingattached to said screw-on faces 16 by means of fastening screws 14, 14′at both sides in the movement direction of the tappet 9. The leafsprings 6, 6′ vary in width; they narrow conically in the longitudinaldirection of the tappet 9, and project beyond the other end 10, whichfaces away from the mounting end II, of the tappet 9, so that they formbetween them, at their ends, a space for holding the feedback lever 3.There, the leaf springs enclose a spherical head 4 of the feedback lever3 which is embodied as a twin-armed lever and is aligned approximatelyperpendicularly to the tappet 9 and its movement direction. The feedbacklever 3 is rotatably mounted on the eccentric bolt 7 and, with its otherend which faces away from the feedback lever head 4, engages in theregulating piston 2.

The dimensions of the tappet 9 are selected such that the thickness ofthe tappet end 10 between the leaf springs 6, 6′ approximatelycorresponds to the diameter of the feedback lever head 4, while adjacentto the screw-on faces 16, the tappet 9 is narrowed under the leafsprings 6, 6′ in such a way that in each case one gap 15 is formedbetween the tappet 9 and the spring 6. In each case one setting screw 13is provided in the region of said gap 15, by means of which settingscrews 13 a degree of bending of the leaf springs 6, 6′ can be set and apreload can be obtained. This is particularly important because it ispossible in this way to set a dead band which is desired when reachingthe neutral position or going beyond the neutral position to a certainextent.

When the regulating piston 2 is adjusted by means of the proportionalmagnets, the feedback lever 3 rotates about the rotational axis set bythe eccentric bolts 7 and, with the feedback lever head 4, pushes one ofthe springs 6, 6′ away from the tappet 9, which therefore generates aforce, which counteracts the setting force of the magnet, on theregulating piston. The adjustment of the regulating piston 2 activatesthe servo system which adjusts the swash plate of the axial pistonengine in the direction of the desired pivot angle. As a result of theadjustment of the swash plate, the tappet 9 also moves in such a waythat the counterforce exerted by the leaf spring increases further, saidcounterforce then prevailing over the setting force of the magnet andreturning the regulating piston until the latter has approximatelyarrived back in its neutral position when the nominal value is reached.

The same reference symbols are also used in the following figures todenote the same structural features. FIG. 2 shows the adjustment devicein section along the regulating piston 2. The proportional magnets 12,12′ act, by means of their tappets 19, 19′, on the end faces of saidregulating piston 2. A longitudinal bore 18 in the regulating piston 2serves to discharge leakage oil. When the regulating piston 2 isdisplaced out of its neutral position, ducts leading to the servo systemare opened or closed.

The feedback lever 3, which is embodied as a twin-armed lever, engages 5by means of its spherical or cylindrical feedback lever base 20 in theregulating piston 2. Here, the engagement point is situated, offsetrelative to the central longitudinal axis 17 of the regulating piston,on the straight connecting lines between the magnet plungers 19, 19′.This avoids tilting moments and resulting undesired force effects on theregulating piston.

The feedback lever 3 is mounted so as to rotate about the pivot axis 5and, as described previously, is held on the feedback lever head 4 inthe space between the ends of two leaf springs 6, 6′ which are attachedat both sides of the tappet 9.

FIG. 3 shows a detailed section from FIG. 2, with the regulating piston2, the feedback lever 3 and the leaf springs 6, 6′ being illustrated,said leaf springs 6, 6′ between them enclosing the feedback lever head4. The regulating piston 2 can be displaced along the axis 17 by meansof the proportional magnets 12, 12′. The feedback lever 3 which isrotatable about the pivot axis 5 engages by means of its base in theregulating piston 2, and is guided there by means of the ball guide 8.The leaf springs 6, 6′ bear against the spherical feedback lever head 4at both sides in the movement direction of the tappet 9 which isconnected to the swash plate, it being possible to apply a preload tosaid leaf springs 6, 6′ by means of the setting screws 13, 13′ in such away that a defined dead band can be provided.

FIG. 4 shows the feedback device 1 as seen in the direction of thelongitudinal extent of the regulating piston 2. The longitudinal bore 18of the latter, for discharging leakage oil, can again be seen. The pivotaxis of the feedback lever 3 is provided by a cylindrical eccentric bolt7 which is mounted in the housing and has an eccentric section on itsmiddle part on which the feedback lever 3 is mounted. Here, theeccentricity is to be dimensioned such that rotation of the eccentricbolt 7 permits a displacement of the pivot axis which is sufficient tobe able to adjust the zero position. The transverse dimension of theleaf spring 6 narrows towards the feedback lever head 4. This is one ofseveral possibilities for fine-tuning the active spring force, thoughthis can also be achieved by means of a varying stiffness in thelongitudinal direction or, if appropriate, suitable bending of the leafsprings. That end of the leaf spring 6 which projects beyond the end 10of the tappet encloses between itself and the opposite leaf spring thefeedback lever head 4 and is fastened to the tappet 9 by means of thefastening screw 14. The setting screw 13 again serves to set a preloadof the leaf spring 6.

The generation of the preload and of a dead band can be gathered in moredetail from FIGS. 5 a and 5 b. FIG. 5 a shows a section A-A from FIG. 4.

The leaf springs 6, 6′ are fastened to the screw-on faces 16, 16′ of thetappet 9 by means of screws 14, 14′. Adjacent to the fastening faces 16,16′, the transverse dimension of the tappet 9, with the exception of itsend 10, is reduced such that in each case one gap 15, 15′ is formedbetween the leaf springs 6, 6′ and the tappet 9.

Setting screws 13, 13′ are provided at a suitable point in the region ofthe gap 15, 15′, by means of which setting screws 13, 13′ the leafsprings 6, 6′ can be clamped against the transverse dimension, which isreduced here, of the tappet 9. The leaf springs 6, 6′ can have acorresponding preload applied to them in this way. If, for example, theunloaded leaf spring 6, 6′ bears against the end 10 of the tappet andagainst the feedback lever 4, it is possible in this way to set adefined dead band which is desired for the regulation of the supplyvolume of axial piston engines. By suitably adapting the geometricdimensions regarding the position of the screw-on faces 16, 16′, of thetappet end 10 and of the feedback lever head 4 in conjunction with theselection of the point at which the setting screws 13, 13′ bridge thegap 15, 15′, it is possible to fine-tune both the spring constants ofthe leaf springs and also the force level which determines the deadband.

1. Axial piston engine having a swash plate, or a bent axis with a valvesegment, which can be adjusted by means of a servo piston, and having anadjustment unit for electrically proportionally adjusting the supplyvolume, said adjustment unit having a regulating piston (2) forcontrolling the oil pressure which moves the servo piston, havingelectrically actuable proportional magnets (12, 12′) which act on theregulating piston (2), and a feedback device (1) for feeding theinstantaneous swash plate position or bent axis valve segment positionback to the regulating piston (2), the feedback device (1) having atappet (9) which is mechanically coupled to the swash plate or to thebent axis valve segment, in each case one leaf spring (6, 6′) beingarranged along each side of said tappet (9), said leaf springs enclosinga feedback lever (3) which is mounted in the regulating piston (2). 2.Axial piston engine according to claim 1, in which the leaf springs (6,6′) have a width and/or stiffness which varies, in particularcontinuously, in the longitudinal direction of the tappet (9).
 3. Axialpiston engine according to claim 1, in which one end of the feedbacklever (3) is mounted in a ball guide (8) in the regulating piston (2),and the feedback lever head (4), which is situated opposite said end, ofthe feedback lever (3) is clamped between the leaf springs (6, 6′). 4.Axial piston engine according to claim 1, in which the leaf springs (6,6′) extend along the tappet (9) and beyond its end (10), and betweenthem, at their ends, form a space for holding the feedback lever (3). 5.Axial piston engine according to claim 2, in which the leaf springs (6,6′) are fastened to the tappet (9) by means of in each case at least onesetting screw (13, 13′), by means of which in each case one preload,with which the leaf springs (6, 6′) act on the feedback lever (3), canbe set, said preload defining a dead band.
 6. Axial piston engineaccording to claim 5, in which the width and/or stiffness of the leafsprings (6, 6′) vary in the longitudinal direction of the tappet in thedirection of the feedback lever (3) in such a way that a desired deadband can be obtained.
 7. Axial piston engine according to claim 6, inwhich the dead band of each leaf spring (6, 6′) can be set individually.8. Axial piston engine according to claim 7, in which the tappet (9) hasscrew-on faces (16, 16′) on the tappet (9), said screw-on faces (16,16′) forming a contact surface for fastening the leaf springs (6, 6′) bymeans of fastening screws (14, 14′), and a gap (15, 15′), by means ofwhich the preloads of the leaf springs (6, 6′) can be set using thesetting screws (13, 13′).
 9. Axial piston engine according to claim 3,in which the feedback lever head (14) is spherical or cylindrical. 10.Axial piston engine according to claim 1, in which the engagement pointof the feedback lever (3) in the regulating piston (2) is situatedoutwith the central longitudinal axis (17) of the latter.
 11. Axialpiston engine according to claim 1, in which the engagement point of thefeedback lever (3) in the regulating piston (2) is situated on thelongitudinal axis of actuating elements which are actuated by theproportional magnets (12, 12′).
 12. Axial piston engine according toclaim 1, in which the regulating piston (2) has a longitudinal bore (18)through which leakage oil can be discharged.
 13. Type series of axialpiston engines according to claim 1 having different supply volumes,with all the models of said type series being provided with the sameadjustment unit.